The long-term goal of this project is to develop an advanced mu/SPECT/CT molecular imaging technology including a state-of-the-art innovative mu/SPECT system and accurate quantitative pinhole and multi-pinhole SPECT imaging techniques that provide ultra-high-resolution down to approximately 0.5 mm and detection efficiency on the order of 2 cps/mu/Ci. To evaluate the novel fSPECT/CT technology, we propose to perform simulations as well as experimental phantom and small animal imaging studies. To respond to the main concern of the reviewers that the previous proposal was too diffuse, we have refocused the research by redesigning the mu/SPECT system configuration with a fixed-angled detector assembly without going through the prototype stage, constructing the unique 'angled detector module assembly' with the latest high performance but robust detector technologies, eliminating the longitudinal tomography study using planar multi-pinhole imaging with standard gamma camera system, deleting two small animal imaging studies to focus on the most important application to imaging of plaques in mice, and switching to a simpler transgenic mouse model with stable and unstable plaques. Also, the proposal is strengthened by additional preliminary data from multi-pinhole image reconstruction, Monte Carlo simulation of pinhole SPECT data, and plaque imaging in transgenic mice using 99mTc Hynic-Annexin V. The team of investigators is streamlined with 2 groups of investigators and 3 key consultants with relevant areas of expertise. The revised specific aims are: (1) to develop a state-of-the-art 'angled' detector module and single and multiple pinhole collimation and an x-ray imaging device for use in the mu/SPECT/CT systems in Aim #5, (2) to develop simulation software for 3D SPECT imaging that models performance characteristics of the scintillation camera modules, design parameters of single and multiple pinhole collimator, and the SPECT system geometry and configuration, (3) to develop 3D quantitative SPECT image reconstruction methods for single and multiple pinhole SPECT with correction of attenuation, scatter and collimator response for accurate absolute quantitation of radioactivity in vivo, (4) to develop simple, accurate and robust calibration methods for single and multi-pinhole SPECT systems, (5) to develop a prototype mu/SPECT/CT system that includes two angled detector assemblies developed in Aim #1 and an existing mu/CT system that will be mounted on a commercial grade CT gantry, and (6) to evaluate the pinhole SPECT imaging techniques and the mu/SPECT/CT system in imaging stable and vulnerable plaques in a transgenic mouse model using 99mTc labeled Annexin-V.